Self-locking fasteners

ABSTRACT

The invention is directed to self-locking screws in which the locking action is produced by at least a part of two adjacent thread convolutions which lean out of normal position toward each other and thereby grip the interposed thread of the mating part.

Stetes Podell et a1.

[ Sept. 26, 1972 [5 1' SELF-LOCKING FASTENERS [72] inventors: Howard 1. Podell, 6 Dawes Place, Larchmont, NY. 10538; Stephen J. Kehoe, Kings Highway, Valley Cottage, NY. 10989 [22] Filed: Aug. 11, 1971 [21] Appl. No.: 170,962

Related US. Application Data [63] Continuation of Ser. No. 842,990, July 18,

1969, abandoned.

[52] US. Cl. ..72/88, 10/10, 10/27, 72/469 [51] Int. Cl. ..B2lh 3/04, B23g 9/00, B21d 17/04 [58] Field of Search ..10/2, 10,11, 27, 86, 86 A; 72/88, 89, 90, 469; 151/22 [56] References Cited UNITED STATES PATENTS I-lanneman ..15 1/22 2,284,659 6/1942 Hosking ..72/88 2,371,365 3/1945 Tomalis et al. 10/10 2,371,463 3/1945 Olson ..72/469 3,196,918 7/1965 Hampton ..l5l/22 3,308,645 3/1967 Hampton ..72/88 3,459,250 8/1969 Tabor ..l5 l/22 3,530,920 9/1970 Podell ..151/22 Primary Examiner-Richard J. Herbst Assistant Examiner-E. M. Combs Attorney-W. Bigelow Hall, Richard A. Wise and Aubrey C. Brine 5 7] ABSTRACT The invention is directed to self-locking screws in which the locking action is produced by at least a part of two adjacent thread convolutions which lean out of normal position toward each other and thereby grip the interposed thread of the mating part.

2 Claims, 11 Drawing Figures PATENTED SEP 26 1972 SHEET 1 0F 4 I 21 V0 n 10 rs Howard 1? Pode/l Step/zen J'Ke/zoe 5 their-,4 ttarrzc SELF-LOCKING FASTENERS This application is a continuation of application Ser. No. 842,990 filed July 18, 1969 and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates generally to improvements in self-locking screws and more particularly to such screws the locking action of which is derived from an irregularity in thread profile produced during the thread rolling operation. Other aspects of the invention relate to a method of treating a screw blank between special thread rolling dies in order to produce the selflocking action, and to the novel dies employed for rolling self-locking screws.

An integral self-locking screw in which the locking action is obtained from a localized departure from normal thread cross section possesses a number of ad-' vantages over a composite one in which the locking action is obtained by means of an insert locked in a cavity or by a patch adhesively secured to threads which are otherwise normally formed. The integral type of selflocking screw can be more economically processed since the locking zone may be formed at the same time as the normal threads. In addition, since the integral type is all metallic, it is better adapted to withstand much higher temperatures and still retain its locking ability under severe vibration environment than can composite self-locking screws in which the locking action is usually derived from plastics which are relatively soft and have low melting points.

A specific advantage of the present invention will best be understood from a preliminary consideration of what happens to a screw thread when the screw is seated, or placed in tension by the tightening of the screw into a mating part. The two opposite flanks of a screw thread, when the screw is seated, are subjected to different effects. Of the two flanks which define a thread, the flank nearest the head of the screw is subjected to a compressive force as it is engaged by the adjacent flank of the female thread of the mating part; whereas the opposite or free flank of the screw, under such conditions, tends to move away from the adjacent flank of the female thread. The force of tighening thus tends to deflect the threads of the screw away from the head of the screw.

In a standard thread, one without deformation or displacement of any sort, the load is distributed over the entire length of the load bearing screw flank in engagement with the nut with the result that thread deflection is thereby minimized. In a self-locking screw having a locking zone in which locking action is produced by a localized change in the thread angle, the effect of engagement of the locking zone with the nut and of seating of the screw is to concentrate the load upon the abnormal portion of the thread and thereby tend to impress upon the originally abnormal thread, a normal thread shape. When the originally abnormal contact flank of the screw is deformed back to a normal thread form under the tension applied during seating, part of the locking action is lost. In order to minimize this loss so as to retain as much of the original locking characteristics as possible after repeated seatings, it has heretofore been necessary that the screw be formed of hard material or of material susceptible to hardening through heat treatment or case hardening. This expedient, however, is not always available or desirable because the screw material may not be of a heat treatable type, or because of the adverse effect that a hardened abnormally shaped male thread may have on the mating female thread, which may be for example a tapped hole in an expensive part, and therefore, not readily replaceable.

SUMMARY OF THE INVENTION It will be seen from the foregoing that an object of the present invention is to provide an integral selflocking screw having a locking zone which is subjected to a minimum re-forming of the thread profile as a result of forces applied thereto during seating.

It is a further object of the invention to provide a self- ]ocking screw which retains a maximum locking action after repeated reuse with a mating part of a hardness comparable to or greater than that of the screw.

Another object of the invention is to provide a selflocking threaded fastener formed of un-heat treated material having a locking zone profile which is substantially unchanged after repeated reuse.

A more general object of the invention is to provide a die configuration for rolling threads by which it is possible to provide one or more locking zones in screws positioned as needed for the specific conditions which will be encountered in use and to do so at minimum cost.

In the achievement of the foregoing objects a feature of the invention relates to an unbalanced form of locking thread profile in which the deviation from normal flank position is greater on the free flank than on the load-bearing or contact flank. This unbalanced profile, which is readily achieved by the novel procedures of the present invention permits the retention of a major portion of the locking action after seating of the screw since the free flank is not appreciably affected by the seating load.

According to a related feature of the invention, the screw which has its free flank a greater distance than the load bearing flank from normal or standard thread position, may also have its locking characteristics enhanced by a coincident localized thickening of the thread. The result is that while opposing flanks of two adjacent threads are disposed at an angle to each other less than the normal angle and thereby frictionally grip the intervening thread of the mating part, the thread on the screw, being locally broader than normal at the pitch diameter, is wedged into the groove of the nut for additional and cumulative locking action. It will be seen from the following detailed description that this latter feature of thickening the thread may either be provided or omitted from a self-locking thread in which maximum departure from normal is on the non-load bearing side. Whether the increased thread thickness is applied to the self-locking portion of the thread or not depends upon the requirements of the application.

DESCRIPTION OF THE DRAWINGS The foregoing objects and features of the invention together with the tools and processes by which the features are realized are more fully described in the following detailed description of an illustrative embodiment of the invention taken in connection with the accompanying drawings in which:

FIG. 1 is a view on an enlarged scale of a screw embodying the feature of one form of the invention;

FIG. 2 is a perspective view of a screw disposed between two rolling dies having a thread rolling surface modified in accordance with the teaching of this invention and partly broken away for clarity;

FIG. 3 is a top plan view of the dies of FIG. 2;

FIG. 4 is a plan view of a rolling face of a thread rolling die of FIGS. 1, 2 and 3;

FIG. 5 is a perspective view showing a section taken on line 5-5 of FIG. 4;

FIGS. 6 to 10 inclusive are successive views illustrating relative positions of a screw and a pair of rolling dies rolling a self-locking screw according to one form of the invention inwhich lock forming areas on the two dies are in phase; and

FIG. 11 is a view on a greatly enlarged scale of a typical thread profile in the locking zone of a screw according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the drawings, particularly FIGS. 1 and 1 1 there is shown a screw indicated generally at having a head 22 and a threaded shank indicated generally at 24. A locking zone on the shank 24 as seen in FIG. 1 comprises part of thread turn 26 which provides locking action when inserted into a nut of standard thread profile as indicated generally at 28 in FIG. 11. In addition to' the convolution 26 whose height and one of whose flank angles are substantially displaced from normal position as seen in FIG. 11 (which is described in detail hereinafter), the adjacent convolution indicated at 30 is also truncated to a lesser degree and is slightly thickened across its flanks which are relatively oriented at the normal thread angle. The thread form, and manner by which it is obtained and the mode of locking will be more fully described hereinafter following a description of the shape of the dies used for rolling the locking thread and the flow of screw shank material as it is being rolled by the dies.

As seen in FIGS. 2 through 5, a headed screw blank 32 is being threaded between rolling dies consisting of a stationary die 34 and a moving die 36. The end of each of the dies which first contacts the screw blank during a rolling operation is called the leading end. Thus as viewed in FIG. 2 the left end of the stationary die 34 and the right end of the moving die 36 designated respectively as 38 and 40 are leading ends whereas the ends 42 and 44 of the stationary and moving dies respectively are trailing ends. Each of the dies 34 and 36 are provided with a plurality of ridges 45 and lock forming portions are formed on each consisting of a notch 46 created by the removal of a ridge 45 from the die as seen more clearly in FIG. 5. In addition to the removal of a ridge 45 from the die, the modification of the dies according to the present invention includes a thinning of a ridge adjacent a notch 46 on the side thereof away from the notch. This is best illustrated in FIG. 5 in which a ridge 48 has been thinned by the removal of stock from its flank 50 on the side away from the notch 46. In practice, one or more ridges 45 may be removed from one die or from both dies of a pair. In one embodiment of the present invention, however, the remote flank of the adjacent ridge is removed, such as by grinding, to an extent and for a purpose which will be more fully described. In another embodiment of the invention the near flank on the second ridge beyond the notch 46 may also be ground away a predetermined amount in order to thicken certain thread portions and improve the locking characteristics of the resulting screw as will be more fully described hereinafter.

In FIGS. 6 to 10 there is shown, enlarged for clarity a screw disposed between rolling dies having lock forming areas which are in phase that is, disposed substantially opposite one another as shown, according to one form of the invention starting from a position in which two more revolutions of the screw will complete the thread rolling operation. It should further be understood that the dies may also be arranged such that the lock forming areas are not disposed opposite one another or out of phase. In these views, FIG. 10 represents the relationship of the screw and the two dies at the point of completion of the thread rolling operation as the completed screw drops from between the dies. FIGS. 9, 8, 7 and 6, respectively, depict the relationships occurring 180, 360, 540 and 720 of rotation of the screw blank before the completion position of FIG. 10. In FIGS. 6 to 10 a die 54 to the right is the stationary die and a die 56 shown to the left, is the moving die. Each of the dies 54, 56 is depicted with two lock forming portions each comprising notches formed by removing a ridge. Thus, the moving die 56 has lock forming areas comprising notches 58 and 60 and the stationary die 54 is shown with lock forming areas comprising notches 62 and 64. In addition, to the notches 58, 60, 62, 64 each of which is part of a lock forming area, there is included as an essential part of each lock forming area a flank of an adjacent ridge from which material has been removed as shown in FIG. 5. Thus, flanks 66, 68, and 72 are coupled respectively with the notches 58, 60, 62 and 64 in comprising lock forming areas on the dies.

In the configuration depicted in FIGS. 6 to 10 there is little coaction between the zones 58 and 62 on the one hand with the zones 60 and 64 on the other. The dies depicted in FIGS. 6 to 10 therefore form two distinct locking zones on a screw rolled between them, one, the product of the thin die flanks 66 and 70 and the notches 58 and 62 and the other resulting from the thin flanks 68 and 72 and the notches 60 and 64. In the description which follows a clearer understanding will be obtained by following the action of the dies upon the screw blank with reference to the upper lock forming areas only.

In FIG. 6 flank portion 76 of the thread being formed is rolled against the reduced flank portion 66 on the die and is therefore rolled to a greater than normal thickness with the additional material being disposed on the upper side of the thread. Similarly, screw flank portion 78 in rolling contact with the reduced die flank 70, also becomes thicker than normal. In discussing the action of the die upon the screw threads being formed on the blank, it is convenient to refer to specific portions of one of the flanks of the screw thread to distinguish it from other portions even though the thread is a continuous helix. Thus, the flank portion 76, which is a continuation of the flank portion 78 is referred to as though it were an independent entity merely for convenience of expression. I

Between FIGS. 6 and 7 the screw blank is rolled by the movement of the die 56 and the enlarged screw flank portion 78 is now located in the notch 58 with the result that the enlargement of the flank portion 78 is not disturbed nor does it have any immediate effect upon the formation of the thread. As depicted in FIG. 7, at the same time that the flank portion 78 is in the space 58, the flank portion 76 is in contact with the reduced die flank portion 70 with the result that the flank portion 76 either retains its enlargement (or completes its enlargement) but is in no other way effected.

In FIG. 8 which depicts the relationship of the screw blank and the dies 180 after FIG. 7; 360 after FIG. 6; and 360 before completion of the thread rolling operation, the enlarged flank portion 76 is centered in the notch 58 and the enlarged flank portion 78 is centered in the notch- 62 with the result that during this portion of the rolling neither enlarged flank portion loses any of its original enlargement.

It is seen in FIG. 9 that the enlarged flank portion 78 has now rolled into engagement with the upper wall of the notch 58, whereas the enlarged flank 76 is centered in the notch 62. The effect of the engagement between the enlarged flank portion 78 and the upper wall of the notch 58 is to cause the corresponding thread portion to be deflected downwardly (away from the head of the screw). As a result the thread groove which is centered in the notch 58 is reduced in its included angle. One of the advantages of the present invention is the fact that the upper thread flank which defines this thread groove, (which is the free or non-load bearing flank) is displaced from its normal position a greater extent than the lower flank because of the previously described deflecting effect of the increased thickness of the flank portion 78. In a co-pending US. Pat. application Ser. No. 731,416, filed by one of the co-applicants of this application and assigned to the assignee of the present invention there is described a process and resultant product characterized by substantially equal deflection or displacement of adjacent thread turns toward one another, with the load-bearing and non-load bearing lock forming area corresponding generally to the'notch 58 defined by a missing ridge. However, by the herein described removal of material from the flank portions 66 and 70 on the dies, it is possible to cause a greater displacement of the locking thread turns from the normal position which will become clear as the description proceeds.

At the same time that the upper flank portion 78 contacts the upper wall of the notch 58 as seen in FIG. 9, the flank portion 76 is centered in the notch 62 and accordingly the shape of the flank portion 76 is not affected during this portion of the operation.

In the position of FIG. 10 the enlarged flank portion 78 has moved into engagement with the upper wall of the notch 62 which causes downward deformation of the corresponding portion of the thread of which 78 is the upper flank, At the same time the part of the thread convolution of which the flank 76 is a part is also being deflected downwardly by the engagement of the flank 76 with the upper wall of the notch 58.

It is seen from the foregoing description that the relative positions of the dies 54 and 56 as depicted in FIGS. 6 to 10 yield coaction between the lock forming zones in the two dies and that the increase in the thickness of the width of the thread forming grooves by removal of material from the flanks of predetermined die ridges causes an increase in the amount of displacement in the thread configuration over and above that obtained according to the above-identified co-pending application of assignee. It has been found that in a die for rolling 96-16 UNC threads, removal of approximately 0.002 inch from the flank of the die ridge produces a screw with excellent locking characteristics. For screws with finer pitches the amount of material removed from the die flank is reduced whereas it is proportionally increased for coarser pitches. The removal of material from the flanks 66 ar'id.70 may be. regarded as the creating of a preparation zone in which a portion of the screw blank is treated before entering the lock forming area comprising the notches 58 and 62. Preparation consists in building up a portion of the flank of the screw thread which portion, later in the rolling operation, will engage the wall of the notch to cause greater deflection of the locking thread turn.

Although a screw with some locking action may be obtained from dies having a single lock forming portion, a die configuration which provides locking zones throughout most of the screw length may be obtained by eliminating every third die ridge as shown in FIGS. 6 to 10, and thinning the flanks 66, 68, 70 and 72 on the far side of the adjacent ridges.

The opposing flank of the next adjacent ridge (designated as 80, 82, 84 and 86 in FIG. 6) may also have portions removed by an amount equal to or different from that removed from the flanks 66, 68, 70 and 72. The effect of reducing the flanks 80, 82, 84 and 86 is to increase the thickness of the thread portions in addition to the above described displacement. For example, the convolution starting between reduced flanks 76 and 80 in FIG. 6 will be thicker than normal when it is completely rolled as shown in FIG. 10 and this increased thickness provides a controlled wedging action in addition tothe locking action obtained by displacement.

Referring again to FIG. 11, the screw 20 of FIG. 1 is shown in detail in spaced relation with the mating nut 28. The screw 20 is shown to have a plurality of normal convolutions 80 each having a load bearing flank 82 and a free flank84 relative to a load bearing surface 86 of the screw head 22. The locking zone comprises the adjacent convolutions 26 and 30 which for purposes of comparison have superimposed thereupon in dotted lines a pair of normal convolutions 88 and 90 respectively. As will be noted, the convolutions 26 and 30 formed by the novel invention are truncated in shape when compared with the convolutions 88, 90 and are substantially displaced from a normal convolution.

The convolution 26 has a free flank 92 and a load bearing flank 94, the load bearing flank being disposed at substantially half the standard thread angle or lying substantially along the free flank of the superimposed normal convolution 88. The adjacent convolution 30 has load bearing flank 96 and a free flank 98, the free flank corresponding substantially with the flank of the superimposed normal convolution 90. It is therefore evident that the forming process as hereinbefore described with regard to FIGS. 6 through 10 is effective to displace the material in the convolutions 26 and 30 substantially between the load bearing flank 94 of the convolution 26 and the free blank 98 of the convolution 30. A pitch line 100 taken along the pitch diameter of the thread and a radial plane 102 passed perpendicular to the centerline of the shank are shown in FIG. 11, to more adequately compare the convolutions 26 and 30 with the normal convolutions 88 and 90. As will be noted, each of the convolutions 26 and 30 are truncated in shape, the convolution 30 being truncated to a lesser degree than the convolution 26. Further, at the pitch diameter which is represented by line 100, the convolution 26 is seen to be substantially broader than the normal convolution 88, while the convolution 30 is only slightly broader than the normal convolution 90, the root thus formed therebetween being formed higher than that formed by two normal turns. One of the more dominant features of the locking zone is best seen by comparing the angle designated as 104 which is produced by the free flank 92 with a free flank of the normal convolution 88, which is designated 106. The angle 104 is substantially less than the angle 106 which is half the thread angle. Thus, the increased thickness of the convolution 26 and the decreased angle of the flank 92 produce an unbalanced thread profile in which the deviation from normal takes place substantially on the free flank 92, rather than on a load bearing flank of the thread form.

Since obvious changes may be made in the specific embodiment of the invention described herein without departing from the'scope thereof, it is intended that all matter contained herein be interpreted in an illustrative and not a limiting sense.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. In the method of rolling threads on a screw blank wherein the blank is rolled between two relatively movable dies each having thread forming working surfaces, which include as thread forming surfaces a series of substantially parallel thread root forming ridges and thread crest forming grooves joined by flank forming walls disposed and spaced at angles corresponding to the particular thread helix angle to be formed, said thread forming surface including a locking zone forming area having a thread root forming ridge removed to adjacent crest forming grooves, and a thread preparation zone comprising the two adjacent thread root forming ridges disposed ahead in rolling sequence of said locking zone forming area wherein at least one of said ridges is relieved along a flank forming wall, the steps of first rolling said blank in said dies beginning uniform, continuous helical thread convolutions on said blank each having a root and a crest joined by flank portions, preparing a thread convolution for subsequent forming into a locking zone by rolling said convolution in said preparation zone, broadening the cross section of said convolution generally at the pitch diameter thereof and shallowing the root adjacent said convolution, and forming a locking zone in a portion of said thread by rolling said prepared thread convolution and an adjacent thread convolution only on opposite outer flanks and not on adjacent inner flanks, wherein the adjacent inner flanks are unsupported in said subsequent rolling, thereby deforming the thread defined between said supported and unsupported flanks by further shallowing the root between said adjacent flanks and steepening thg slope of said adjacent flanks by deflecting said threa convolution toward said adjacent convolution in an axial direction.

2. A die for rolling threads on a screw blank wherein threads fonned include a locking zone, comprising a base portion and a thread forming surface on said base portion, said thread forming surface having a series of substantially parallel thread root forming ridges and thread crest forming grooves joined by flank forming walls disposed and spaced at angles corresponding to the thread helix angle to be formed, a locking zone forming area proximate the screw exit end of said thread forming surface and a thread preparation zone disposed ahead in rolling sequence of said locking zone forming area, said locking zone forming area including a pair of parallel thread root forming ridges separated by a region having a thread root forming ridge removed to adjacent thread crest forming grooves, and said thread preparation zone including a pair of parallel thread root forming ridges, one ridge of which is one of said pair of parallel thread root forming ridges of said locking zone forming area and the second ridge of which is the next adjacent thread root forming ridge, in which preparation zone at least one of the flank forming walls of said ridges is relieved from its root forming ridge to its crest forming groove whereby one of the two adjacent thread convolutions subsequently entering said locking zone forming area is broadened in its cross section generally at the pitch diameter thereof and shallowed at its root in said preparation zone prior to said two adjacent threads being rolled only on opposite outer flanks and not on adjacent inner flanks by said flank forming walls in said locking zone forming area.

P0405 UNITED STATES PATENT OFFICE 569 cmirimr or eeEerroN Patent 3,695 ,3 9 Dated September 26, 1972 Inventor(s) Howard 1 eodei E Stephen J. Kehoe It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Ti tie After inventors, insert -Assignee; ugM corporation,

Boston, Massachusetts- Signed and sealed this 22nd day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. In the method of rolling threads on a screw blank wherein the blank is rolled between two relatively movable dies each having thread forming working surfaces, which include as thread forming surfaces a series of substantially parallel thread root forming ridges and thread crest forming grooves joined by flank forming walls disposed and spaced at angles corresponding to the particular thread helix angle to be formed, said thread forming surface including a locking zone forming area having a thread root forming ridge removed to adjacent crest forming grooves, and a thread preparation zone comprising the two adjacent thread root forming ridges disposed ahead in rolling sequence of said locking zone forming area wherein at least one of said ridges is relieved along a flank forming wall, the steps of first rolling said blank in said dies begiNning uniform, continuous helical thread convolutions on said blank each having a root and a crest joined by flank portions, preparing a thread convolution for subsequent forming into a locking zone by rolling said convolution in said preparation zone, broadening the cross section of said convolution generally at the pitch diameter thereof and shallowing the root adjacent said convolution, and forming a locking zone in a portion of said thread by rolling said prepared thread convolution and an adjacent thread convolution only on opposite outer flanks and not on adjacent inner flanks, wherein the adjacent inner flanks are unsupported in said subsequent rolling, thereby deforming the thread defined between said supported and unsupported flanks by further shallowing the root between said adjacent flanks and steepening the slope of said adjacent flanks by deflecting said thread convolution toward said adjacent convolution in an axial direction.
 2. A die for rolling threads on a screw blank wherein threads formed include a locking zone, comprising a base portion and a thread forming surface on said base portion, said thread forming surface having a series of substantially parallel thread root forming ridges and thread crest forming grooves joined by flank forming walls disposed and spaced at angles corresponding to the thread helix angle to be formed, a locking zone forming area proximate the screw exit end of said thread forming surface and a thread preparation zone disposed ahead in rolling sequence of said locking zone forming area, said locking zone forming area including a pair of parallel thread root forming ridges separated by a region having a thread root forming ridge removed to adjacent thread crest forming grooves, and said thread preparation zone including a pair of parallel thread root forming ridges, one ridge of which is one of said pair of parallel thread root forming ridges of said locking zone forming area and the second ridge of which is the next adjacent thread root forming ridge, in which preparation zone at least one of the flank forming walls of said ridges is relieved from its root forming ridge to its crest forming groove whereby one of the two adjacent thread convolutions subsequently entering said locking zone forming area is broadened in its cross section generally at the pitch diameter thereof and shallowed at its root in said preparation zone prior to said two adjacent threads being rolled only on opposite outer flanks and not on adjacent inner flanks by said flank forming walls in said locking zone forming area. 